diff --git a/contract/models/account_move.py b/contract/models/account_move.py
index 29ec3f0ce5..a20c75c9ae 100644
--- a/contract/models/account_move.py
+++ b/contract/models/account_move.py
@@ -10,4 +10,4 @@ class AccountMove(models.Model):
     _inherit = "account.move"
 
     # We keep this field for migration purpose
-    old_contract_id = fields.Many2one("contract.contract")
+    old_contract_id = fields.Many2one("contract.contract", index=True)